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Linux - Virtualization and Cloud This forum is for the discussion of all topics relating to Linux Virtualization and Linux Cloud platforms. Xen, KVM, OpenVZ, VirtualBox, VMware, Linux-VServer and all other Linux Virtualization platforms are welcome. OpenStack, CloudStack, ownCloud, Cloud Foundry, Eucalyptus, Nimbus, OpenNebula and all other Linux Cloud platforms are welcome. Note that questions relating solely to non-Linux OS's should be asked in the General forum.

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Old 11-08-2010, 10:18 PM   #1
pinga123
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How many VCPUs?


We have purchased four intels xeon processors

http://ark.intel.com/Product.aspx?id=46491

As per the specification each cpu has 6 cores therefore we have 24 cores (considering 4 cpus).
Now how would i calculate the number of vcpus that can be used while virtualization?
This will help use to capacity planning.

Quote:
specification is as below.

Intel® Xeon® Processor E7530
(12M Cache, 1.86 GHz, 5.86 GT/s Intel® QPI)
SPECIFICATIONS
Essentials
Status Launched
Launch Date Q1'10
Processor Number E7530
# of Cores 6
# of Threads 12
Clock Speed 1.866 GHz
Max Turbo Frequency 2.133 GHz
L3 Cache 12 MB
Intel® QPI Speed 5.86 GT/s
Embedded Options Available
No
Supplemental SKU No
Max TDP 105 W
VID Voltage Range 0.675V-1.35V
Tray 1ku Budgetary Price $1446.00
Package Specifications
TCASE 64°C
Sockets Supported FCLGA1567
Halogen Free Options Available Yes
Advanced Technologies
Intel® Turbo Boost Technology
Yes
Intel® Hyper-Threading Technology
Yes
Intel® Virtualization Technology (VT-x)
Yes
Intel® 64
Yes
Enhanced Intel SpeedStep® Technology
Yes
Execute Disable Bit Yes

Last edited by pinga123; 03-29-2012 at 06:03 AM.
 
Old 11-09-2010, 06:58 PM   #2
Soadyheid
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Might this not depend on the Virtualisation software you're using? I've only played about with Sun/Oracle's VirtualBox where you don't actually have to assign resources to each virtual machine apart from disk space. I don't know if VMware's hypervisor needs hardware configuration.
It might also depend on what you actually want to do with your Virtual systems. If it's doing a lot of I/O work, maybe one core is enough, if you're running queries on multiple databases you might want to assign two or more cores.
What are you fitting the CPUs into? HP, DELL, etc. You might also want to consider one of Virtualisations problems... You generally have a single point of failure. I've had an HP system with apparently 50 odd virtual machines on it crash when one of four CPUs failed - the master one. Unlike Sun Sparc or IBM PowerPC processors, the CPUs don't just de-configure and the system reboots and/or keeps on running. Can your Virtualisation software dynamically migrate the systems to a second host should the main host fail? If so, remember when planning loading that the second host would have to have the spare capacity to cope.
Hmmm... Interesting stuff to think about!

Play Bonny!
 
Old 11-09-2010, 11:05 PM   #3
pinga123
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Quote:
Originally Posted by Soadyheid View Post
Might this not depend on the Virtualisation software you're using? I've only played about with Sun/Oracle's VirtualBox where you don't actually have to assign resources to each virtual machine apart from disk space. I don't know if VMware's hypervisor needs hardware configuration.
It might also depend on what you actually want to do with your Virtual systems. If it's doing a lot of I/O work, maybe one core is enough, if you're running queries on multiple databases you might want to assign two or more cores.
What are you fitting the CPUs into? HP, DELL, etc. You might also want to consider one of Virtualisations problems... You generally have a single point of failure. I've had an HP system with apparently 50 odd virtual machines on it crash when one of four CPUs failed - the master one. Unlike Sun Sparc or IBM PowerPC processors, the CPUs don't just de-configure and the system reboots and/or keeps on running. Can your Virtualisation software dynamically migrate the systems to a second host should the main host fail? If so, remember when planning loading that the second host would have to have the spare capacity to cope.
Hmmm... Interesting stuff to think about!

Play Bonny!
We are using Oracle's VM (Which is a not same as Oracle's Virtual Box).
We used to assign Ram and VCPU before creating a new Virtual Machine.
I dont have any idea on how to calculate VCPUs? (Considering we have 24 cores(from 4 physical CPUs))
 
Old 11-10-2010, 06:53 PM   #4
Soadyheid
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Quote:
I dont have any idea on how to calculate VCPUs? (Considering we have 24 cores(from 4 physical CPUs
Hmmm... Each CPU has 12 threads so you effectively have 48 "CPUs"

Might it work like IBM's PowerPC processors where you can microslice a CPU to assign 1/1000th of a CPU to a LPAR? What's Oracle's definition of a VCPU? The fact that you define "Virtual CPUs" implies that you can split your resource however you want to so I'd make the lowest value either one core or one thread, 24 or 48, then decide how many cores or threads you want to assign to each virtual machine.

Sorry, does that make sense? I don't feel not going to be of much help to you.

Play Bonny!
 
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Old 11-11-2010, 12:28 AM   #5
pinga123
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Quote:
Originally Posted by Soadyheid View Post
Hmmm... Each CPU has 12 threads so you effectively have 48 "CPUs"

Might it work like IBM's PowerPC processors where you can microslice a CPU to assign 1/1000th of a CPU to a LPAR? What's Oracle's definition of a VCPU? The fact that you define "Virtual CPUs" implies that you can split your resource however you want to so I'd make the lowest value either one core or one thread, 24 or 48, then decide how many cores or threads you want to assign to each virtual machine.

Sorry, does that make sense? I don't feel not going to be of much help to you.

Play Bonny!
Well your explanation may not solve the purpose but you have correctly mentioned Thread role which was quite new.
I guess there is no rule for deciding VCPU as not all virtual guests are designed to perform in similar fashion.
Moral of discussion:
You have to decide VCPU count based on following factor.
1)If its a production server with lot of CPU oriented application it will be better to assign VCPU's equal to Number of CPU Core.
2)For a test or non production environment You can always play with figure and consider threading to determine VCPU count.

Correct me if i m wrong.

Last edited by pinga123; 11-11-2010 at 12:29 AM.
 
Old 11-11-2010, 12:39 PM   #6
scheidel21
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I agree with Pinga as a general rule I don't hand out more VCPUs than I have physical CPUs especially not in a production machine. In most cases depending on how many servers or VMs you want to run I would hand out 2-4 per machine maybe two if using a client OS like XP, VISTA, 7, Linux Workstation. and four to Server OSes, Server 08, 03, Linux servers.
 
Old 11-11-2010, 06:22 PM   #7
Soadyheid
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Quote:
As per the specification each cpu has 6 cores therefore we have 24 cores (considering 4 cpus).
Now how would i calculate the number of vcpus that can be used while visualization?
The information you have so far not included is the number of Virtual Machines you intend to install on the host and their use.

I would reckon if it was something more than 48 VMs then you'd have to have some way to microslice the processors - effectively a sort of round robin time slice system. 48 or less you consider threads or cores. Less than 10 you can assign multiple threads or cores dependent on the VMs purpose.

Like I mentioned before, I don't know of any Intel/AMD based system which can handle a failed CPU dynamically so you risk loosing all the VMs should one fail. Maybe someone can enlighten me.

So how many hosts do you have anyway? Are you fitting all 4 CPUs in one host or 2 in two hosts? Maybe you've got 4 hosts with one CPU per?
I'd reckon you'd need to know how many VMs you need plus what resources are available to give a decent answer.

Play Bonny!
 
  


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